Radar system and method for detecting hazards associated with particles or bodies

ABSTRACT

The hazard warning system includes processing system for detecting an HVB condition. The aircraft warning system can use at least two types of radar returns and can measure decorrelation time to detect the HVB condition. Warnings of HVB conditions can allow an aircraft to avoid threats posed by such conditions including damage to aircraft equipment and engines.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is related to U.S. application Ser. No.14/681,901 filed on Apr. 8, 2015, U.S. Pat. No. 9,323,291, which is acontinuation of U.S. application Ser. No. 13/246,769 filed on Sep. 27,2011, U.S. Pat. No. 9,019,146,291, U.S. application Ser. No. 14/206,651filed on Mar. 12, 2014, U.S. Pat. No. 9,720,082, U.S. application Ser.No. 14/086,844 filed on Nov. 21, 2013, U.S. Pat. No. 9,720,082, U.S.application Ser. No. 13/919,406 filed on Jun. 17, 2013, U.S. Pat. No.9,244,157, U.S. application Ser. No. 13/841,893 filed Mar. 15, 2013,U.S. Pat. No. 9,244,166, U.S. application Ser. No. 14/207,304 filed onMar. 12, 2014 invented by Koenigs, et al., U.S. Pat. No. 9,823,347, U.S.application Ser. No. 13/246,769 filed Sep. 27, 2011, U.S. Pat. No.9,019,146, and U.S. application Ser. No. 14/206,239, filed on Mar. 12,2104 invented by Sishtla, et al., U.S. Pat. No. 9,864,055, allincorporated herein by reference in their entireties and assigned to theassignee of the present application.

BACKGROUND

Conventional aircraft hazard weather radar systems, such as the WXR 2100MultiScan™ radar system manufactured by Rockwell Collins, Inc., haveDoppler processing and are capable of detecting at least fourparameters: weather range, weather reflectivity, weather velocity, andweather spectral width or velocity variation. The weather reflectivityis typically scaled to green, yellow, and red color levels that arerelated to rainfall rate. The radar-detected radial velocity variationcan be scaled to a turbulence level and displayed as magenta. Suchweather radar systems can conduct vertical sweeps and obtainreflectivity parameters at various altitudes.

Particles and bodies such as high altitude ice crystals (HAIC), volcanicash, and birds (HVB), pose threats to aircraft and their components.Particles can also include smoke clouds from forest fires. For example,sensors can provide improper readings when clogged by ice or otherparticles. Probes and engines can also be susceptible to damage causedby mixed phase and glaciated ice crystals when operating near areas ofdeep convection and at higher altitudes, caused by ingestion of one ormore birds into the engine, or caused by operation in clouds associatedwith smoke or ash from forest fires or volcanic activity. Enginerollback issues are believed to be related to ice crystal accretion,followed by aggregate detachment in solid form before continuing throughthe aircraft engine.

Conventional X-band radar systems have insufficient per pulse energy onthe target to detect and discriminate HVB based upon reflectivity levelsalone especially at longer ranges. Distinguishing low reflectivityprecipitation areas from areas of high altitude associated threat(HAAT), high altitude ice crystal (HAIC) formation and HAIC clouds(HAIC²) and other small particle clouds can be difficult. Detection anddisplay of conditions associated with ice crystals, smoke, volcanic ash,and birds are desirous because such conditions can have a direct impacton aircraft, crew and passengers depending on the severity.

Thus, there is a need for an aircraft hazard warning system and methodthat senses ice crystals, smoke, volcanic ash, and birds (e.g., HVB)conditions. There is also a need for a hazard detection system thatdetects and displays warnings associated with ice crystals, smoke,volcanic ash, and birds. There is also a need for a weather radar systemand method for detecting low density particle clouds driven byatmospheric turbulence. There is further a need for a weather radarsystem and method for detecting low density particle condition atsufficient range to allow aircraft to avoid the condition. Yet further,there is a need for a low cost, light weight, low power aircraft hazardwarning system that alerts a pilot to warnings associated with icecrystals, smoke, volcanic ash, and birds.

It would be desirable to provide a system and/or method that providesone or more of these or other advantageous features. Other features andadvantages will be made apparent from the present specification. Theteachings disclosed extend to those embodiments which fall within thescope of the appended claims, regardless of whether they accomplish oneor more of the aforementioned needs.

SUMMARY

In certain aspects, embodiments of the inventive concepts disclosed aredirected to an aircraft hazard warning system. The aircraft hazardwarning system includes a processing system detecting an HVB conditionusing at least two types of radar signals (e.g., two or more types offrequency or two or more types of polarization). The processing systemprovides a number of pulses at a pulse repetition frequency via a radarantenna system and receives radar return data associated with the numberof pulses via the radar antenna system.

In further aspects, embodiments of the inventive concepts disclosed aredirected to a method of using a radar system to detect a particlecondition. The method includes determining a number of pulses per dwellfor a first decorrelation time of radar returns, providing the number ofpulses at a pulse repetition frequency via a radar antenna system, andreceiving radar return data associated with the number of pulses via theradar antenna system. The method also includes determining if asignal-to-noise ratio of returns associated with the dwell is above athreshold, and processing the radar return data to detect the particlecondition.

In further aspects, embodiments of the inventive concepts disclosed aredirected to an aircraft weather radar system. The aircraft weather radarsystem includes a radar antenna for receiving radar returns, and anelectronic processor configured to detect a particle cloud. Theelectronic processor provides a number of pulses at a pulse repetitionfrequency via the radar antenna and receives radar return dataassociated with the number of pulses via the radar antenna. The numberof pulses is chosen in response to a measured decorrelation time of theradar returns.

Another exemplary embodiment relates to an aircraft weather radarsystem. The aircraft weather radar system includes a radar antenna forreceiving radar returns, and an electronic processor determining an HVBcondition in response to at least two types of radar returns.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments will become more fully understood from thefollowing detailed description, taken in conjunction with theaccompanying drawings, wherein like reference numerals refer to likeelements, and:

FIG. 1 is a perspective view schematic illustration of an aircraftcontrol center, according to some embodiments;

FIG. 2 is a side view schematic illustration of the nose of an aircraftincluding a radar system, according to some embodiments;

FIG. 3 is a schematic block diagram of the radar system illustrated inFIG. 2 including a particle detector, according to some embodiments;

FIG. 4 is a schematic representation of a radar signal comprised of alook (which is comprised of a number of dwells which are each comprisedof a number of pulses) for the radar system illustrated in FIG. 3,according to some embodiments;

FIG. 5 is a chart showing probability of detection versussignal-to-noise ratio (SNR) per look for a Swerling 1 target for theradar system illustrated in FIG. 3 according to some embodiments;

FIG. 6 is a chart showing probability of detection versussignal-to-noise ratio (SNR) per look for a Swerling 2 target for theradar system illustrated in FIG. 3 according to some embodiments;

FIG. 7 is a chart showing coherent integration gain per pulse for 3, 10,30, and 100 pulses per dwell for the radar system illustrated in FIG. 3according to some embodiments;

FIG. 8 is a chart showing frequency change to decorrelate radar crosssection of an ice particle cloud versus particle size for a number ofcloud densities for the radar system illustrated in FIG. 3 according tosome embodiments;

FIG. 9 is a flow diagram showing a particle detection operation for theradar system illustrated in FIG. 3 according to some embodiments;

FIG. 10 is a more detailed block diagram of a single channel,multi-polarization radar system for use as the radar system illustratedin FIG. 3 in accordance with some embodiments;

FIG. 11 is a more detailed block diagram of a dual channel,multi-polarization radar system for use as the radar system illustratedin FIG. 3 in accordance with some embodiments;

FIG. 12 is a more detailed perspective view schematic drawing of a dualband radar system for use as the r radar system illustrated in FIG. 3 inaccordance with some embodiments;

FIG. 13 is a more detailed top view schematic drawing of a dual bandwedge antenna for use with the radar system illustrated in FIG. 12 inaccordance with some embodiments; and

FIG. 14 is a more detailed top view schematic drawing of a smart conefor use with the r radar system illustrated in FIG. 3 in accordance withsome embodiments.

DETAILED DESCRIPTION

Referring generally to the FIGURES, systems and methods for indicating aweather threat to an aircraft are described, according to an exemplaryembodiment. An airborne weather radar system is generally configured toproject radar beams and to receive radar returns relating to theprojected radar beams in some embodiments. The projected radar beamsgenerally pass through air and reflect off of targets (e.g., rain, snow,birds, ice crystals, smoke, ash etc.). Using the reflected return data,processing electronics associated with the weather radar system candetect the targets and the type of targets in some embodiments. Theweather radar system is advantageously configured to display thedetected conditions (e.g., HVB conditions) using indicators of thedetected conditions in some embodiments. For example, the weather radarsystem can provide HVB threat warnings to allow pilots to avoid regionsdetrimental to aircraft and their engines.

In some embodiments, the hazard warning system uses a multiplepolarization and/or multi frequency techniques to detect particleclouds, such as HVB, by matching the polarization ellipse to theorientation and shape of the small particles (e.g., at lowconcentrations (less than or equal to 1 g/m³ for ice and less than orequal to 0.1 g/m³ for ash)). For example, the ability to measurehydrometer shape and orientation allows discrimination of thermodynamicphase of water and ice particles. In some embodiments, the weather radarsystem detects low-density threatening particle clouds (e.g., ice orvolcanic ash) at long range so that aircraft can be steered aroundthreat. The weather radar system employs frequency hopping todecorrelate scattering from the cloud from dwell to dwell (e.g., using acarrier frequency range of plus or minus four or eight MHz is sufficientto decorrelate radar cross section (RCS) under most conditions) in someembodiments.

In some embodiments, the weather radar system takes advantage ofturbulence coherence times to perform coherent integration within adwell as minimum coherence times are expected to be on the order ofmilliseconds, thereby allowing multiple pulse coherent integration witha greater than 1 kilohertz (kHz) pulse repetition frequency (PRF)waveform. The turbulence decorrelates RCS over the period of multipledwells in some embodiments. In some embodiments, a mixture of coherentand non-coherent processing is selected to increase probability ofdetection (e.g., based on coherent integration loss of 1 dB or less forrepresentative atmospheric turbulence spectra or based on optimum numberof non-coherent dwells per cloud observation).

Referring now to FIG. 1, an illustration of an aircraft control centeror cockpit 10 is shown for an aircraft 101, according to an exemplaryembodiment. The aircraft control center 10 includes flight displays 20which are generally used to increase visual range and to enhancedecision-making abilities. In an exemplary embodiment, the flightdisplays 20 may provide an output from a warning system (e.g., a radarsystem 300 (FIG. 2)) of the aircraft. For example, the flight displays20 may provide a top-down view, a horizontal view, verticalview/perspective or 3 dimensional view, or any other view of weather,small particle conditions and/or terrain detected by the radar system300 on the aircraft. The aircraft control center 10 may further includeother user interface elements such as an audio device (e.g., speaker,electro-acoustic transducer, etc.) and illuminating or flashing lamps.Weather can be displayed as colored regions on the aircraft 101according to weather radar standards. In some embodiments, one or moreof a HAIC, HAIC², HAAT, bird, smoke, or ash, or other particle conditionwarning can be provided on any of the displays 20 as part of a weatherradar display.

Referring to FIG. 2, the front of the aircraft 101 is shown withaircraft control center 10 and nose 100, according to an exemplaryembodiment. The radar system 300 (e.g., a weather radar system or otherradar system) is generally located within nose 100 of aircraft 101 orwithin aircraft control center 10 of aircraft 101. According to variousexemplary embodiments, the radar system 300 may be located on the top ofaircraft 101 or on the tail of the aircraft 101 instead. The radarsystem 300 may include or be coupled to an antenna system 310. A varietyof different antennas or radar circuits may be used as part of system300 (e.g., a split aperture antenna, a monopulse antenna, a sequentiallobbing antenna, active electronically scanned antenna array (AESA),passive electronically scanned antenna array (PESA), etc.). In certainembodiments, the antenna system 310 is a dual or more than dualfrequency antenna and/or a dual or more than dual polarization antenna.

The radar system 300 sweeps a radar beam 104, 106 horizontally back andforth across the sky. The radar system 300 conducts a first horizontalsweep (e.g., the beam 104) directly in front of the aircraft 101 and asecond horizontal sweep (e.g., the beam 106) downward at some tilt angle108 (e.g., 20 degrees down) in some embodiments. The sweep can includeradar signals at multiple frequencies or polarizations. The radar system300 can be a WXR-2100 MultiScan™ radar system or similar systemmanufactured by Rockwell Collins and configured as described herein.According to other embodiments, the radar system 300 can be an RDR-4000system or similar system manufactured by Honeywell International, Inc.configured as described herein. The radar system 300 may be integratedwith other avionic equipment and user interface elements in aircraftcontrol center 10 (e.g., the flashing lights, the displays 20, displayelements on a weather radar display, display elements on a terraindisplay, the audio alerting devices, navigation systems, TAWs equipment,etc.).

Referring to FIG. 3, a block diagram of the radar system 300 embodied asa weather radar system is shown, according to an exemplary embodiment.The radar system 300 is shown to include the antenna system 310connected (e.g., directly, indirectly) to an antenna controller andreceiver/transmitter circuit 302. The antenna controller andreceiver/transmitter circuit 302 may include any number of mechanical orelectrical circuitry components or modules for steering a radar beam.For example, the antenna controller and receiver/transmitter circuit 302can be configured to mechanically tilt the antenna in a first directionwhile mechanically rotating the antenna in a second direction. In otherembodiments, a radar beam may be electronically swept along a first axisand mechanically swept along a second axis. In yet other embodiments,the radar beam may be entirely electronically steered (e.g., byelectronically adjusting the phase of signals provided from adjacentantenna apertures, etc.). The antenna controller andreceiver/transmitter circuit 302 can be configured to conduct the actualsignal generation that results in a radar beam being provided from theradar antenna system 310 and to conduct the reception of returnsreceived at the radar antenna system 310. Radar return data is providedfrom the antenna controller and receiver/transmitter circuit 302 to theprocessing electronics 304 for processing. For example, the processingelectronics 304 can be configured to interpret the returns for displayon the displays 20.

The processing electronics 304 can also be configured to provide controlsignals or control logic to antenna controller and receiver/transmittercircuit 302. For example, depending on pilot or situational inputs, theprocessing electronics 304 can be configured to cause the antennacontroller and receiver/transmitter circuit 302 to change behavior orradar beam patterns. In other words, the processing electronics 304 caninclude the processing logic for operating the radar system 300. Itshould be noted that the processing electronics 304 may be integratedinto the radar system 300 or located remotely from the radar system 300,for example, with other equipment or as stand-alone equipment in theaircraft control center 10.

The processing electronics 304 are further shown as connected toaircraft sensors 314 which may generally include any number of sensorsconfigured to provide data to the processing electronics 304. Forexample, the sensors 314 could include temperature sensors, humiditysensors, infrared sensors, altitude sensors, a gyroscope, a globalpositioning system (GPS), communication units, or any otheraircraft-mounted sensors that may be used to provide data to theprocessing electronics 304. It should be appreciated that the sensors314 (or any other component shown connected to the processingelectronics 304) may be indirectly or directly connected to theprocessing electronics 304. The processing electronics 304 are furthershown as connected to avionics equipment 312 and include a particledetector 340. The particle detector 340 detects and locates at least oneof a HAIC condition, a HAIC² condition, a HAAT condition, a smokecondition, a bird condition, an ash condition or other small particleconditions in the atmosphere associated with the aircraft 101 and causesone or more of the displays 20 to provide a visual and/or audio warningof such conditions. The particle detector 340 processes data associatedwith weather radar reflectivity levels and/or data from other sensors(e.g., temperature, altitude, external weather data from a communicationunit, etc.) to provide appropriate beams for detecting the particleconditions and to detect the particle conditions. The conditions can besensed via a dual or more frequency or dual or more polarization processas explained below and in the applications incorporated herein byreference according to various exemplary embodiments. In someembodiments, the particle detector 340 determines a suitabledecorrelation time of the radar returns and adjusts the waveformprovided by the radar system 300 using the antenna controller andreceiver/transmitter circuit 302 and the radar antenna system 310 sothat probability of detection of HVB or other particle conditions isincreased.

The avionics equipment 312 can be or include a flight management system,a navigation system, a backup navigation system, communication units, oranother aircraft system configured to provide inputs to processingelectronics 304. The avionics equipment can provide weather data fromexternal sources in some embodiments. The processing electronics 304 maybe or include one or more microprocessors, an application specificintegrated circuit (ASIC), a circuit containing one or more processingcomponents, a group of distributed processing components, circuitry forsupporting a microprocessor, or other hardware configured forprocessing. In some embodiments, processing electronics 304 areconfigured to execute computer code, a routine or module to complete andfacilitate the activities described herein associated with the particledetector 340.

The radar return data processed by the particle detector 340 can bestored according to a variety of schemes or formats. The radar returnsare stored in time so that decorrelation time can be measured. Forexample, the radar return data may be stored in an x,y or x,y,z format,a heading-up format, a north-up format, a latitude-longitude format, aradial format, or any other suitable format for storing spatial-relativeinformation. The particle detector 340 can use any of the techniquesdescribed in U.S. application Ser. Nos. 14/086,844, 14/207,034,14/206,239, 13/919,406 and 13/84893 incorporated herein by reference intheir entireties to process the radar return data and provide a warning.

In some embodiments, the particle detector 340 includes logic for usingradar returns to make one or more determinations or inferences regardingthreats related to particle conditions. The particle detector 340 andthe radar system 300 can be configured to use dual or multi frequency ordual or multi polarization processes to detect presence of the particlecondition and its location in some embodiments. The dual or multifrequency and dual or multi polarization techniques advantageously allowfor providing information on the nature of the scattering environment.The particle detector 340 and the radar system 300 can utilize aninferred or non-inferred process discussed in related U.S. patentapplication Ser. No. 14/206,239 incorporated herein by reference in someembodiments. In one embodiment, the particle detector 340 and the radarsystem 300 receives data associated with weather returns and processesthe data to determine existence of a particle condition. The data can beprocessed by comparing the data representing returns of a first type(e.g., polarization or frequency) and returns of a second type (e.g.,polarization or frequency) to known return characteristics to determinea match to the condition. In some embodiments, the data can be processedto determine existence of Swerling 1 or Swerling 2 targets which providean indication of whether a low density particle cloud is present (e.g.,an ice condition, an ash condition, a smoke condition, etc.)

With reference to FIG. 4, the radar system 300 provides a radar beamincluding a look 400. The look 400 includes a number of dwells 402(N_(D)) which each include a number of pulses 404. The number of dwells402 can be an integer from 1 to N in some embodiments. The number ofpulses 404 (N_(P)) in each dwell 402 can be an integer from 1 to M insome embodiments. M and N can be any integer 1, 2, 3, . . . , 10, . . ., 100, . . . . The pulses are provided at a pulse repetition frequency(PRF). Each of the pulses 404 is defined by duration of “transmitter on”time for pulsed radar such as the radar system 300. Each of the dwells402 is defined by a time of duration over which pulse returns arecoherent. The look 400 is defined by the time of duration of dedicateddetection observations. The radar system 300 selects a number of pulsesand the pulse repetition frequency in accordance with a decorrelationtime to detect HVB and other particle conditions in some embodiments.The pulses can by at varying frequencies and polarities. The radarsystem 300 selects a number of dwells in accordance with atmospheric toincrease probability of detect HVB detection in some embodiments. Thepulses can be at varying frequencies and polarities in some embodiments.Within a dwell, the frequency and polarization are constant. From dwellto dwell, the frequency may change to force radar cross section (RCS)fluctuations in some embodiments. The frequency and polarization maychange from look to look in some embodiments.

Particles in the atmosphere can be categorized as Swerling 1 target anda Swerling 2 target in some embodiments. The Swerling 1 target has anexponential distribution of RCS across look to look, and the Swerling 2Target has an exponential distribution of RCS across dwell to dwell insome embodiments. Swerling 1 or 2 RCS statistics are achieved when theRCS is comprised of many scatterers, no one of which is dominant in someembodiments. Swerling 1 or 2 RCS statistics indicate particle clouds insome embodiments. The Doppler power spectral density (PSD) can be usedto determine the dwell to dwell decorrelation in some embodiments (e.g.,Swerling 1 or Swerling 2).

With reference to FIG. 5, a chart 600 for a Swerling 1 target includes aY axis 602 representing probability of detection and an X axis 604representing signal-to-noise ratio (SNR) per look in decibels (dBs).Graphs 606, 608, 610, 612, and 614 are provided for a look with thenumber of dwells equal to 1, 2, 4, 8 and 16 (N_(D)=1, 2, 4, 6, 8, and16) respectively. Chart 600 shows that an optimum number of dwells perlook is one assuming that the energy on target per look is constant andis without radar cross section fluctuations in some embodiments For afixed total energy on target per look, providing a number of dwellsgreater than 1 reduces the probability of detection for Swerling 1targets in some embodiments.

With reference to FIG. 6, a chart 700 for a Swerling 2 target includes aY axis 702 representing probability of detection and an X axis 704representing signal-to-noise ratio (SNR) per look in decibels (dBs).Curves 706, 708, 710, 712, and 714 are provided for a look with thenumber of dwells equal to 1, 2, 4, 8 and 16 (N_(D)=1, 2, 4, 6, 8, and16) respectively. Chart 700 shows that an optimum number of dwells(N_(D)) per look is four assuming that the energy on target per look isconstant and is without radar cross section fluctuations within a dwellbut fluctuates independently from dwell to dwell. A probability between0.6 to 0.9 requires a signal-to-noise ratio of 13.6 dB to 16.6 dB perlook with N_(D) equal to four in some embodiments. Frequency hopping canbe used to decorrelate the RCS dwell to dwell to achieve Swerling 2statistics in some embodiments. In some embodiments, a carrier frequencyrange of plus or minus four or plus or minus eight MHz is sufficient todecorrelate RCS under most conditions. The responses using differentnumbers of dwells (N_(D)) can be analyzed with respect to charts 600 and700 to classify Swerling 1 and 2 targets.

With reference to FIG. 7, a chart 800 represents an environmental limiton the coherent integration period and includes a Y axis 802representing coherent integration gain per pulse (G_(cl)/N_(p)) and an Xaxis 804 representing the ratio of the coherent integration time to thedecorrelation time on a logarithmic scale on a logarithmic scale. Thecoherent integration time (T_(SL)) equals N_(P)/PRF where PRF is thepulse repetition frequency. The coherent integration gain (G_(cl))equals N_(P) for T_(CL)<<τ₀. Graphs 806, 808, 810, and 812 are providedfor a look with the number of pulses per dwell equal to 3, 10, 30, and100 (N_(P)=3, 10, 20, and 100), respectively. For atmosphericturbulence, coherent integration period (i.e., dwell period) should beno longer than t₀/2 in some embodiments. In some embodiments, theatmosphere decorrelates RCS dwell-to-dwell and Swerling 2 statistics areachieved. Table 1 below shows the coherent integration time perdecorrelation time (T_(CL)/τ₀) for 1 dB and 3 dB losses for PowerSpectral Density associated with a Gaussian spectrum, an f⁻⁴ spectrum,and a von Karmen spectrum. The f⁻⁴ spectrum is between the Gaussianspectrum and the von Karmen spectrum.

TABLE 1 Environmental Limit on Coherent Integration Period PowerSpectral Density 1-dB Loss (NP > 10) 3-dB Loss (NP > 10) Gaussian TCI/τ₀≤ 1.3 TCI/τ₀ ≤ 2.9 f-4 TCI/τ₀ ≤ 1.1 TCI/τ₀ ≤ 2.8 von Karmen  TCI/τ₀ ≤0.48 TCI/τ₀ ≤ 2.4

With reference to FIG. 8, a chart 900 includes a Y axis 902 representingfrequency change in megahertz (MHz) on a logarithmic scale and an X axis904 representing particle size in millimeters on a logarithmic scale.Lines 906, 908, 910, 912 and 914 are provided for clouds having an iceconcentration (C) of 0.1 grams per meter cubed (g/m³), 0.3 g/m³, 1.0g/m³, 3.0 g/m³, and 10 g/m³, respectively. The frequency change requiredto change phase relationship by π/4 of adjacent particles separated bymean distance l is given by the following equation:ΔΦ=2πl/λ₂−2λl/λ₁=2πlΔf/c=π/4 where Δf=c/8l; where c is speed of light.The mean number of particles per unit volume is n˜1/l³; wheren=C/ρ_(ε)πD₀ ³/6; C=Mass concentration (g/m³); ρ_(ε)=density of theparticle (g/m³); and D₀=Average particle size. The required frequencychange to decorrelate RCS is equal to: Δf=c/8[C/ρ_(ε)πD₀ ³/6]^((1/3)).Accordingly, frequency hops of plus or minus four or eight MHz aroundcenter frequency are sufficient for the radar system to decorrelateice/ash cloud RCS except at unreasonably high concentrations or smallmean particle sizes in some embodiments.

With reference to FIG. 9, the processing electronics 304 and theparticle detector 340 (FIG. 3) can operate according to a flow 1000 fordetecting particle conditions such as HVB or smoke conditions. At anoperation 1002, the radar system 300 and the particle detector 340selects a representative decorrelation time τ₀ of atmospheric turbulence(e.g., based on empirical observations). In some embodiments, τ₀ is 10to 100 milliseconds. The operation 1002 can begin after the radar system300 has identified a suspect area in some embodiments. The suspect areacan be input by a user, provided by an external source (e.g., from otheraircraft or a terrestrial source), or sensed by the radar system 300 insome embodiments. In some embodiments, low level reflectivity levels orcell formations (e. g., cumulonimbus anvil regions) associated with HAICareas can indicate a suspect area.

At an operation 1004, the radar system 300 and the particle detector 340choose the number of pulses per dwell N_(P) so T_(Dwell)=N_(P)/PRF=τ₀/2in some embodiments, where PRF is pulse repetition frequency andT_(Dwell) is the period of the dwell. At the operation 1004, the radarsystem 300 and the particle detector 340 provide the radar signal,receive the radar returns and determine the SNR per dwell (SNR_(Dwell))where SNR_(Dwell)=N_(P)*SNR_(P) wherein SNR_(P) is the signal-to-noiseratio of a return pulse. At an operation 1006, if the SNR_(Dwell) isgreater than 10.6 dB, the radar system 300 and the particle detector 340proceed to an operation 1008. If not, the radar system 300 and theparticle detector 340 proceed to an operation 1007. At the operation1007, if the pulse repetition frequency can be increased (the pulserepetition frequency has not reached its maximum), the radar system 300and the particle detector 340 proceed to an operation 1014 and increasethe pulse repetition frequency to achieve 10.6 dB SNR_(Dwell). Afteroperation 1014, the radar system 300 provides pulses according to theoperation 1004. At the operation 1007, if the pulse repetition frequencycannot be increased (the pulse repetition frequency has reached itsmaximum), the radar system 300 and the particle detector 340 proceed toan operation 1018 and increase the number of dwells per look (N_(D))(e.g., according to FIG. 6 to increase the signal to noise ratio perlook and to achieve the desired probability of detection (>0.6)). Afterthe operation 1018, the radar system 300 provides pulses according tothe operation 1004.

At the operation 1008, the radar system 300 and the particle detector340 process four dwells per look to achieve optimum detection. Eachdwell can be at different frequency and/or separated sufficiently intime to decorrelate the radar cross section. At an operation 1010, theradar system 300 and the particle detector 340 measure decorrelationtime and repeat operations 1004-1010 with a better choice for the dwellperiod (i.e., number of coherent pulses per dwell) at an operation 1012.

The decorrelation period or time can be measured in the operation 1010according to a variety of techniques. Autocorrelation of a time historyof pulses can be used to measure the decorrelation time (e.g., the 1/epoint of the autocorrelation function) in some embodiments. A Fouriertransform on received return data can be used to determine how quicklythe atmosphere is changing for a decorrelation time. For example, aFourier transform on return pulses provides a Doppler spread that is aninverse measure of the decorrelation time.

In the operation 1008, the dwells are processed to determine thepresence of HVB conditions. Generally, particles in a HVB condition havevarious sizes and shapes. Cross sectional area of targets using dualpolarization techniques can be used to discriminate the type HVBcondition in some embodiments. Relatively larger sizes in the horizontaldirection as opposed to the vertical direction indicate icing conditionswhile ash conditions have less oblong shapes in some embodiments.Further, bird targets can be discriminated by larger sizes in someembodiments. Responses at various frequencies and comparisons thereofcan be compared to empirical data to discriminate types of HVBconditions in some embodiments. For non-spherical ice particles, theradar cross section (RCS) depends on polarization in some embodiments. Hpolarization has an e-vector in the X-Y plane, and vertical polarizationhas an e-vector in the Z direction.

Frequency diversity provides additional information on particle sizesand ice water content for more accurate discrimination and fewer falsealarms in one embodiment. Due to differences in scattering regimes suchas Rayleigh and Mie scattering, particles have different radarreflectivities at different wavelengths. Comparison of reflectivity fortwo or more frequencies provides information on average particle size.For example, transition from Rayleigh and Mie scattering depends onfrequencies and particle shape to a minor extent. Comparison ofreflectivity for two or more frequencies provides information on theaverage particle size in a fixed particle size cloud.

In some embodiments, returns can be compared to historical returncharacteristics at varying polarizations and frequencies to determine amatch. The historical returns can be provided on a location by locationor geographic type basis (e.g., continental, maritime, etc.). In oneembodiment, ice particles in globe-like sphere form have a longdimension that is aligned in accordance with aerodynamic forces and/orelectric fields associated with weather cells. Generally, a largervariation between horizontal and vertical polarization can mean a higherprobability of ice presence. By comparing returns in horizontal orvertical polarizations, asymmetric particles can be distinguished fromsymmetric particles (e.g., super cooled water drops) or cloudscontaining asymmetrical particles (e.g., ice) can be distinguished fromclouds not containing asymmetric particles.

Generally, larger particle sizes indicate a presence of ice as supercooled water tends to be small and spherical. Accordingly, the dualfrequency technique provides information about size of particles fordetermination of a HAIC² and HAIC condition. In one embodiment, thefrequency difference between the two bands is large to provide betterdistinction between returns and particle sizes. Cross sectional area oftargets using dual polarization techniques can be used to discriminatethe type HVB condition in some embodiments. Responses at variousfrequencies and comparisons thereof can be compared to empirical data todiscriminate types of HVB conditions in some embodiments.

In some embodiments, the flow 1000 can use information from othersensors to improve detection of HVB conditions. In some embodiments, theflow 1000 can use satellite cloud top information to identify anexpected location for ice and satellite infrared information on volcanicash extent to identify an expected location for ash. Positiveidentification from multiple sensors can be used to increase confidencein detection and improve detection. A lack of external sensor data canbe used to reduce false alarms (e.g., if the satellite sensor does notsee any clouds, then the radar system 300 may disqualify an icecondition warning).

With reference to FIG. 10, a single channel, multi-polarization radarsystem 1100 can be used in the radar system 300. The radar system 1100includes a weather radar receiver (WxR) 1102, a local oscillator 1104, awaveform generator 1106, a transmit amplifier 1100, a duplexer 1112, asingle channel azimuth/elevation joint 111, and an antenna system 1120.The radar receiver can provide I and Q data associated with radarreturns to the electronic processor 304 in some embodiments. The antennasystem 1120 includes a polarization switch 1116 a horizontalpolarization element 1126 and a vertical polarization element 1124. Arepresentation 1128 shows the horizontal polarization element 1126 andthe vertical polarization element 1124. In some embodiments, the antennasystem 1120 is a mechanically scanned waveguide antenna. Thepolarization switch 1116 can configure the antenna system 1120 forvertical polarization, horizontal polarization or 45 degree slantlinear. The polarization switch 1116 can have a horizontal polarizationport and a vertical polarization port, each of which can be switched onand off. This architecture enables tri-state polarization detection in asingle channel in a relatively inexpensive radar system. The variouslypolarized radar returns are sufficiently correlated as long as thepolarization switch has an appropriate switching speed. By comparing thereturns in the three polarization states (horizontal, vertical and45-degree), estimates can be made of the deviation of the particles fromspherical shapes, an indicator of particle type, and orientation of thelong particle axis if non-spherical shape. Non-horizontal orientation ofparticles is an indication of strong vertical winds or strong electricfields, both of which can be dangerous to aircraft.

An X-band rotary joint can be removed if radio frequency circuitry ismounted to the back of antenna system 1120. In some embodiments, singlechannel rotary joints are utilized. The antenna system 1120 can includean antenna array, such as those disclosed in U.S. Pat. Nos. 8,098,189and 7,436,361 incorporated herein by reference in their entirety, anactive electronically scanned array (AESA), or a passive electronicallyscanned array (PESA). The antenna system 1120 can be a dual orthogonallinear polarization (DOLP) antenna using DOLP strip line slots, DOLPmicro strip patches, or interlaced waveguide sticks radiators for DOLPin some embodiments.

With reference to FIG. 11, a dual channel, multi-polarization radarsystem 1200 can be used in the radar system 300. The dual channels canbe DOLP channels calibrated for the same insertion loss and phase lossin some embodiments. The radar system 1200 includes a weather radarreceiver (WxR) 1206, a waveform generator 1204, a transmitter 1202, atwo polarization duplexer 1208, a two channel azimuth/elevation joint1222, and an antenna system 1220. The antenna system 1220 includes ahorizontal polarization antenna element 1224 and a vertical polarizationantenna element 1226. The two channel azimuth/elevation joint 1222provides simultaneously horizontal and vertical polarization returns andcan be comprised of two horizontally abutted single axis rotary jointsand two vertically stacked single axis rotary joints in some embodiments

In some embodiments, the transmitter 1202 includes a verticalpolarization channel 1232 including a vertical polarization amplifier1240, a variable gain amplifier 1242, and a variable phase shifter 1244.In some embodiments, the transmitter 1202 includes a horizontalpolarization channel 1234 including a horizontal polarization amplifier1246.

In some embodiments, the receiver 1206 includes a vertical polarizationchannel 1252 including a limiter 1260, a filter 1262, low noiseamplifier 1264, a polarization calibration circuit 1266, and a verticalpolarization receiver 1272. The polarization calibration circuit 1266includes a variable phase shifter 1268, and a variable gain amplifier1270. In some embodiments, the receiver 1206 includes a splitter 1290and an oscillator 1292. In some embodiments, the receiver 1206 includesa horizontal polarization channel 1254 including a limiter 1280, afilter 1282, a low noise amplifier 1284, and a horizontal polarizationreceive 1286. The electronic processor 304 (FIG. 3) can receive theradar return data from the receivers 1286 and 1272.

With reference to FIG. 12, a dual band, single polarization radar system1400 can be used in the radar system 300. The radar system 1400 includesa coherent W-band weather radar transmitter/receiver 1402, a coherentX-band weather radar transmitter/receiver 1404, and an antenna system1420. The antenna system 1420 includes an X-band single polarizationantenna 1430 and a W-band single polarization antenna 1452. The W-bandantenna 1452 can be disposed in the X-band antenna 1430. The antennas1430 and 1452 can be multipolarization antennas, and thetransmitter/receivers 1402 and 1404 can include multiple channels foreach polarization. The processing electronics 304 (FIG. 3) can receivethe radar return data from the X-band coherent receiver 1431 in someembodiments. In some embodiments, the dual band, single polarizationradar system 1400 provides completely coherent systems for multiplefrequency band and multiple polarizations, all derived off a commonreference signal. An existing X Band radar product line can be used aplatform for the radar system 1400 with modifications to the X Bandradar portion as described herein and shown in FIG. 12.

In some embodiments, the coherent X-band weather radartransmitter/receiver 1404 includes a waveform generator 1421, a coherentup/down converter 1422, an X-band coherent transmitter 1426, an X-bandcoherent receiver 1431, a transmitter derivation circuit 1428, aduplexer 1440, and a receiver derivation circuit 1442. In someembodiments, the coherent W-band weather radar transmitter/receiver 1402includes an amplifier 1480, a filter 1482, an up converter 1484, afilter 1486, a transmit amplifier 1488, a duplexer 1490, a receive lownoise amplifier 1492, a down converter 1494, and an X-band low noiseamplifier 1496. In some embodiments, the coherent W-band weather radartransmitter/receiver 1402 receives an X-band transmit signal from thetransmitter derivation circuit 1428 from which a W-band transmit signalis provided via the filter 1482, the up converter 1484, the filter 1486,the transmit amplifier 1486, and the duplexer 1488. In some embodiments,the coherent W-band weather radar transmitter/receiver 1402 uses anX-band receive signal from the receiver derivation circuit 1428 to downconvert a W-band receive signal to an X-band receive signal provided viathe down converter 1494 and the X-band low noise amplifier 1496 to thereceiver 1430. The W-band signal is received via the duplexer 1490 andthe amplifier 1492, is down converted by the down converter 1494 andprovided by the X-band low noise amplifier 1496 to the X-band coherentreceiver 1431.

In some embodiments, radar system 1400 can provide and receive signalsin the C band or the Ka band. The radar system 1400 can be a X/Ka, X/S,or X/C system in some embodiments. Processing for the dual bands can beslaved together with a common processor for both bands or a masterprocessor driving transmitter/receivers 1402 and 1404.

In some embodiments, the W-band antenna element 1452 and the X-bandantenna element 1230 are AESAs or PESAs in some embodiments. In someembodiments, the two channel architecture associated with radar system1200 can be applied to system 1400 to provide a multiband, multichannel,multipolarization system.

With reference to FIG. 13, the antenna system 1420 can be a wedge shapedantenna system 1500 including a W-band vertical polarization PESA 1502,a W-band horizontal polarization PESA 1502, and one or more X-band dualor single polarization AESA panels 1506. The W-band verticalpolarization PESA 1502 and the W-band horizontal polarization PESA 1502can be disposed on a blunt nose 1510 of antenna system 1500.

With reference to FIG. 14, a nose cone 1600 can be provided with panelantennas for the radar system 300. The nose cone 1600 can be used toprovide antenna systems 1420 and 1500 in some embodiments. The nose cone1600 is discussed in U.S. Pat. No. 9,118,112, incorporated herein byreference. Panels 1602, 1604, 1606, and 1608 can be AESA or PESAantennas for the radar system 300 (FIG. 3) in some embodiments. Thepanels 1602, 1604, 1606, and 1608 can be multipolarization and/ormultiple band antennas in some embodiments.

Independent radar systems for dual polarization, or dual/tri-bandfrequency diversity, or both can be self-contained coherent systems insome embodiments. In some embodiments, the ratio of phase can also beutilized for both dual polarization and/or dual frequency systems.Specific differential phase (e.g., between vertical polarization andhorizontal polarization) can be used to identify characteristicsassociated with HVB conditions in some embodiments.

The construction and arrangement of the systems and methods as shown inthe various exemplary embodiments are illustrative only. Although only afew embodiments have been described in detail in this disclosure, manymodifications are possible (e.g., variations in sizes, dimensions,structures, shapes and proportions of the various elements, values ofparameters, mounting arrangements, use of materials, colors,orientations, etc.). For example, the position of elements may bereversed or otherwise varied and the nature or number of discreteelements or positions may be altered or varied. Accordingly, all suchmodifications are intended to be included within the scope of thepresent disclosure. The order or sequence of any process or method stepsmay be varied or re-sequenced according to alternative embodiments.Other substitutions, modifications, changes, and omissions may be madein the design, operating conditions and arrangement of the exemplaryembodiments without departing from the scope of the present disclosure.

According to various exemplary embodiments, electronics 304 may beembodied as hardware and/or software. In exemplary embodiments where theprocesses are embodied as software, the processes may be executed ascomputer code on any processing or hardware architecture (e.g., acomputing platform that can receive reflectivity data from a weatherradar system) or in any weather radar system such as the WXR-2100 systemavailable from Rockwell Collins, Inc. or an RDR-400 system availablefrom Honeywell, Inc. The processes can be performed separately,simultaneously, sequentially or independently with respect to eachother.

While the detailed drawings, specific examples, detailed algorithms andparticular configurations given describe preferred and exemplaryembodiments, they serve the purpose of illustration only. The inventionsdisclosed are not limited to the specific forms and equations shown. Forexample, the methods may be performed in any of a variety of sequence ofsteps or according to any of a variety of mathematical formulas. Thehardware and software configurations shown and described may differdepending on the chosen performance characteristics and physicalcharacteristics of the weather radar and processing devices. Forexample, the type of system components and their interconnections maydiffer. The systems and methods depicted and described are not limitedto the precise details and conditions disclosed. The flow charts showpreferred exemplary operations only. The specific data types andoperations are shown in a non-limiting fashion. Furthermore, othersubstitutions, modifications, changes, and omissions may be made in thedesign, operating conditions, and arrangement of the exemplaryembodiments without departing from the scope of the invention asexpressed in the appended claims.

Some embodiments within the scope of the present disclosure may includeprogram products comprising machine-readable storage media for carryingor having machine-executable instructions or data structures storedthereon. Such machine-readable storage media can be any available mediawhich can be accessed by a general purpose or special purpose computeror other machine with a processor. By way of example, suchmachine-readable storage media can include RAM, ROM, EPROM, EEPROM, CDROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium which can be used to carryor store desired program code in the form of machine-executableinstructions or data structures and which can be accessed by a generalpurpose or special purpose computer or other machine with a processor.Combinations of the above are also included within the scope ofmachine-readable storage media. Machine-executable instructions include,for example, instructions and data which cause a general purposecomputer, special purpose computer, or special purpose processingmachine to perform a certain function or group of functions. Machine orcomputer-readable storage media, as referenced herein, do not includetransitory media (i.e., signals in space).

What is claimed is:
 1. An aircraft hazard warning system, comprising: aradar system comprising a radar antenna; and a processing systemconfigured to detect a presence of smoke from forest fires, highaltitude crystals, volcanic ash, or birds posing a threat to aircraft,the presence being an HVB condition, the processing system beingconfigured to detect the HVB condition using at least two types of radarsignals associated with the radar system, the radar system configured toprovide radar pulses via the radar antenna with an initial dwell periodand receive radar returns associated with the radar pulses via the radarantenna, wherein the processing system is configured to measure adecorrelation time of the received radar returns and to choose a newdwell period based on the decorrelation time, and provide a number ofthe radar pulses for each of a plurality of dwells for provision offuture pulses based upon the new dwell period.
 2. The aircraft hazardwarning system of claim 1, wherein the two types of radar signalsinclude a first radar signal at a first frequency and a second radarsignal at a second frequency.
 3. The aircraft hazard warning system ofclaim 2, wherein the HVB condition comprises an HAIC, HAIC², volcanicash or a presence of birds condition and is detected using the at leasttwo types of radar signals after a region of interest is identified. 4.The aircraft hazard warning system of claim 2, wherein the firstfrequency is an X-band frequency and the second frequency is a C, S, Ka,or W-band frequency.
 5. The aircraft hazard warning system of claim 1,wherein the radar antenna comprises a weather radar antenna.
 6. Theaircraft hazard warning system of claim 5, wherein the decorrelationtime is measured using a Fourier transform of radar return dataassociated with the received radar returns.
 7. An aircraft hazardwarning system, comprising: a radar system; a processing circuitconfigured to detect a presence of smoke from forest fires, highaltitude crystals, volcanic ash, or birds posing a threat to aircraft,the presence being an HVB condition, the processing circuit beingconfigured to detect the HVB condition using at least two types of radarsignals, the radar system being configured to provide radar pulses via aradar antenna of the radar system with an initial dwell period and toreceive radar returns associated with the radar pulses via the radarantenna, wherein the processing circuit is configured to: measure afirst decorrelation time of the received radar returns; choose a newdwell period based on the first decorrelation time; choose a number ofpulses per dwell based on the new dwell period of the radar returns fora future provision of the pulses per dwell; receive radar return dataassociated with the radar returns associated with the number of pulsesper dwell provided via the radar antenna of the radar system; determineif a signal-to-noise ratio of the radar returns associated with thenumber of pulses per dwell is above a threshold; and process the radarreturn data to detect a particle condition.
 8. The aircraft hazardwarning system of claim 7, further comprising: a display, wherein thedisplay is configured to provide a warning of a HAIC condition on aweather radar display.
 9. The aircraft hazard warning system of claim 7,wherein the processing circuit is configured to: measure a measureddecorrelation time using the radar return data; and select the number ofpulses per dwell using the measured decorrelation time from the radarreturn data for another future provision of the pulses per dwell. 10.The aircraft hazard warning system of claim 7, wherein the processingcircuit is configured to increase a pulse repetition frequency for thefuture provision of the pulses if the signal-to-noise ratio per dwell isbelow the threshold.
 11. The aircraft hazard warning system of claim 7,wherein the processing circuit is configured to provide an HVB warningin response to detection of the particle condition.
 12. An aircrafthazard warning system, comprising: a radar system; a processing systemconfigured to detect a presence of smoke from forest fires, highaltitude crystals, volcanic ash, or birds posing a threat to aircraft,the presence being an HVB condition using at least two types of radarsignals, the radar system configured to provide a radar pulses via aradar antenna and to receive radar returns associated with the radarpulses via the radar antenna, wherein the processing system isconfigured to measure a decorrelation time of the received radar returnsand choose a new dwell period based on the decorrelation time, andprovide a number of the radar pulses per dwell based on the new dwellperiod for provision of future pulses.
 13. The aircraft hazard warningsystem of claim 12 further comprising: a display configured to provideweather images, the display providing a warning of a particle cloud. 14.The aircraft hazard warning system of claim 13, wherein the processingsystem uses multifrequency processing to detect the particle cloud. 15.The aircraft hazard warning system of claim 14, wherein a pulserepetition frequency is increased if a signal-to-noise ratio per dwellis below a threshold.
 16. The aircraft hazard warning system of claim13, wherein the radar antenna is an array antenna.
 17. The aircrafthazard warning system of claim 12, wherein the radar signals are weatherradar signals.
 18. The aircraft hazard warning system of claim 12,wherein the radar signals are in an X-band.
 19. The aircraft hazardwarning system of claim 12, wherein the presence is of the volcanic ash.